Commercially available weight filling machines are of two types: with or without integrated tank for distributing the filling product.
The machines of the first type comprise a tank, usually placed on the rotating part of the filler, above the dispensing valves which fill the containers. Thereby, a flap is achieved, which, if the level in the distribution tank is maintained substantially constant, ensures a constant filling speed. The control of the product level inside the tank is mandated to a modulating valve of the pneumatic type which controls the product flow. Other solutions adopted to maintain constant or change the final filling flap as desired consist of the modulation of the gas pressure in the head space of the tank.
Although this type of filling machine is the most widely employed for the reasons set out above, it has, however, several disadvantages. First of all, it is a scarcely flexible system, since, when changing the filling product is desired, the washing and sterilizing operations require a long time, an additional wash circuit, the provision of spray balls and, in the case of aseptic machines, a management system for the sterilization of the gas pressurization assembly as well. Furthermore, in the case of highly viscous or two-phase products, the tank must be equipped with agitators or scrapers and, in the first case, the pressure in the tank may be so high as to require a certification of the tank itself. The bigger the tank is, the more evident these drawbacks are.
Therefore, a second type of weight filling machine has been proposed, in which the distribution tank is eliminated and the regularity of the flow dispensed is provided by a volumetric pump which draws from a remote tank. A simplified diagram of such a machine is shown in FIG. 1.
This machine has a simple layout, significantly reduces washing and sanitation times when changing the filling product, and does not require dedicated washing circuits. However, the diffusion thereof is limited by greater operational management difficulties, especially in the case of non-compressible products. In fact, the control of the flap is difficult to be implemented, especially in the production start and stop steps or in case a filling valve is to be excluded or reactivated, resulting in a sudden change in the dispensing pressure and, therefore, also in the relative speed.
Especially in the case of non-compressible products, the volumetric pump should be capable of restoring the filling valves output volume in real time. A misalignment or a delay in this dynamic implies an immediate and undesirable change in the filling pressure. Also in the hypothesis that the pump will perfectly re-integrate the output product, any change of product speed will result in a change in pressure at the dispensing valves level due to the dynamic pressure, essential to the acceleration/deceleration of the product itself.
In conclusion, filling machines without integrated tank do not allow the same operating results, in terms of precision of the filling flap, obtainable with fillers with integrated tank. A non-constant filling flap results into a non-constant dispensing speed and therefore in a complex management of the filling operations.
Currently, therefore, such a type of machine has been used only for products with high viscosity or which, due to air content or intrinsic features, are partially elastic.